The end of Republican Sen. Richard Lugar's 35-year career representing Indiana in the U.S. Senate could be imminent.

A new Howey/DePauw Indiana Battleground Poll shows the octogenarian trailing State Treasurer Richard Mourdock by 10 percentage points ahead of Tuesday's GOP Senate primary. The survey also finds that the venerable Lugar is increasingly viewed by home-state voters in a negative light.

If Tea Party-favorite Mourdock emerges victorious next week, it will be due in no small part to the anti-tax, free-market advocates at the Washington-based Club for Growth. The Club's political action committee targeted Lugar early, branding him as too liberal on fiscal issues and pumping more than $1.7 million into efforts to defeat him.

It has been a classic Club campaign: underwriting a primary challenge to an entrenched Republican deemed not sufficiently in line with the group's stringent free-market ideals. The Club's tactics have caused intra-party strife, most notably in 2010, when its pick in the Nevada GOP senate race, Sharron Angle, lost to the politically vulnerable Democrat, Senate Majority Leader Harry Reid.

We spoke Friday with Barney Keller of the Club for Growth about the Indiana race and divisions in the GOP. Here's an edited version of our conversation.

NPR: The Club for Growth, in teaming up with Tea Party candidates in 2010, had some great Senate successes, including the election of Ron Johnson in Wisconsin and Pat Toomey in Pennsylvania. But what many remember is Angle's loss in Nevada to Democrat Reid. Polls in Indiana seem to suggest that if your efforts to help oust Lugar are successful, it would boost the chances of Indiana Democratic Senate candidate Rep. Joe Donnelly, and be a factor in potentially denying Republicans control of the Senate again. What goes into your "is it worth it" calculation?

Keller: The premise that [Richard] Mourdock winning the Republican primary in Indiana would make it more likely that the Democrat would win is simply incorrect. The Obama campaign is not going to be contesting Indiana this year like they did in 2008, when they won it by only 2 percentage points — the first time a Democrat whose last name wasn't Bayh had won statewide in Indiana since 1964. Without Obama seriously contesting Indiana, and with a strong fiscal conservative in [gubernatorial candidate] Mike Pence at the top of the ticket, we strongly believe that Hoosier Republicans in November will reject Joe Donnelly's support for Obamacare and the stimulus.

NPR: How does the Club choose its political targets?

Keller: We only get involved in about 15 to 25 races a year where we feel like we can be the difference maker, and also where we feel like there is enough of a difference between the two candidates. In this case we felt like there was a big difference between Sen. Lugar and Richard Mourdock. The common knock against the Club is that we make it easier for Democrats to win. Aside from Sharron Angle, there's really no other example that anybody can point to in all of the races where all of that supposedly happened. The Republican Party should actually thank the Club for Growth. Why does the Republican establishment continue to support liberal Republicans who don't advance conservative policy ideas?

NPR: Republican House Majority Leader Eric Cantor and his "Young Guns" network have taken considerable heat from you and others for encouraging Democrats to vote in Tuesday's open primary to help Lugar's effort. Will this damage Cantor going forward with House Tea Party conservatives, and, if so, how?

Keller: Regrettably, Eric Cantor's actions just confirm the worst of what grass-roots conservatives dislike about a Washington Republican leadership more interested in protecting its own than in promoting conservative politics and conservative candidates. We've seen a Republican leadership that's played not to lose instead of aggressively trying to cut spending and lower the debt. They've gone in the opposite direction by giving Obama the power to raise the debt ceiling by trillions of dollars. We're trying to change that by helping pro-growth, free-market conservatives win elective office through our PAC.

NPR: Has this damaged Cantor's credibility with the Tea Party caucus in the House?

Keller: The idea that anybody in the Republican leadership has been particularly friendly to the Tea Party is a misnomer. There's a common misperception among the mainstream media that because many candidates were elected with Tea Party support in 2010, that means that now that they're in Congress they're promoting fiscally conservative policies. The Republican leadership only cares if you have an "R" next to your name. The Club's PAC actually cares what sort of policies you're going to promote once you get to Congress.

NPR: How has the political ground changed since 2010, when the Tea Party movement fueled the Republican landslide? Now, you have Cantor's group putting out an ad touting Lugar's "mainstream Indiana values" and encouraging Democrats to vote for him in the open primary. You have the public even more disillusioned with Congress, and nonpartisan scholars Thomas Mann and Norman Ornstein blaming Republicans for do-nothing, hyperpartisan Capitol Hill.

Keller: I don't think it has changed at all. The same composition of the Republican Party still wants to see fiscal conservatives and people who believe in a free-market philosophy go to Congress and fight for their beliefs. I'm familiar with the Mann and Ornstein piece. But when has there ever been a bipartisan bill that has cut the size of government? Both parties over the past 20 years have ballooned the size of government at a breakneck speed to a point where we're in a fiscal crisis. We can't continue the same failed policies where the Democrats spend all the money they take in, and the Republicans only spend a little bit less than the Democrats.

NPR: Has the Tea Party lost its fervor?

Keller: I think that the narrative that the Tea Party has declined is kind of a media-driven fascination. Yes, there are no rallies on Congress calling for the repeal of Obamacare anymore. But as you're seeing in Indiana, and other places, people are fed up with Congress, they're fed up with the big spenders in Washington and are looking for pro-growth champions who are going to bring about the type of systemic budget reform that the Club supports.

NPR: If you were sitting in a room with Arizona Sen. John McCain and Chamber of Commerce President Tom Donahue, both of whom have backed Lugar, how would you persuade them to vote for Mourdock? (Lugar is one of 19 senators to earn a 100 percent rating from the Chamber for his votes in 2011.)

Keller: I wouldn't pitch Sen. McCain or Tom Donahue because they simply don't believe in the same things that we believe in. Sen. McCain voted against the Bush tax cuts. The Chamber of Commerce backed the Wall Street bailout and the Obama stimulus. There's a big difference between what establishment pro-business Republicans believe, and in what conservative pro-free market conservatives believe. That's the divide you're seeing in many of these races

NPR: If Lugar loses, how important would you say the Club for Growth will have been in ending his three-plus decades representing Indiana in Washington?

Keller: Richard Mourdock deserves most of the credit. He ran a strong, hardworking, diligent, committed and principled campaign. He deserves much of the credit for presenting a clear contrast on the issues. We were able to help Richard Mourdock get the message out about Sen. Lugar's record. When our PAC makes an endorsement, we're asking our 75,000 members to make an investment in that race. And our members trust us to only endorse candidates that are going to carry the torch of free-market thinking in Congress.